Switched boundary condition (XBC) in FDTD

A new type of boundary condition is introduced in the letter that takes advantage of nonstationary terminations of the finite-difference time-domain (FDTD) mesh. Three techniques are combined to achieve low cost absorbing boundary conditions with excellent properties: frequency up-conversion, inherent FDTD property of dissipation of energy at frequencies close to Nyquist limit, and semi-transparent wall to trap high frequency energy traveling away from the boundary at cell diagonals. The boundary achieves very high absorption levels within two to three FDTD cells. The performance of the boundary is tested in a rectangular waveguide. The goal of this research is to open up a new direction in absorbing boundary research that can lead to efficient absorption with very low memory and numerical costs.